This invention relates generally to semiconductor processing and more specifically to the deposition of a metal layer, such as copper, within a chemical vapor deposition (CVD) system, using a liquid precursor.
In the formation of integrated circuits (ICs) it is often necessary to deposit thin material layers or films, such as films containing metal and metalloid elements, upon the surface of a substrate, such as a semiconductor wafer. One purpose of such thin films is to provide conductive and ohmic contacts for the ICs and to yield conductive or barrier layers between the various devices of an IC. For example, a desired film might be applied to the exposed surface of a contact hole formed in an insulating layer of a substrate, with the film passing through the insulating layer to provide plugs of conductive material for the purpose of making electrical connections across the insulating layer.
One well known process for depositing such films is chemical vapor deposition (CVD), in which a film is deposited on a substrate using chemical reactions between various constituent or reactant gases, referred to generally as process gases. In a CVD process, reactant gases are pumped into a process space of a reaction chamber containing a substrate. The gases react in the process space proximate a surface of the substrate, resulting in the deposition of a film of one or more reaction by-products on the surface. Other reaction by-products that do not contribute to the desired film on the exposed substrate surfaces are then pumped away or purged by a vacuum system coupled to the reaction chamber.
One variation of the CVD process, which is also widely utilized in IC fabrication, is a plasma-enhanced CVD process or PECVD process in which one or more of the reactant process gases is ionized into a gas plasma to provide energy to the reaction process. PECVD is desirable for lowering the processing temperatures of the substrate and reducing the amount of thermal energy usually necessary for a proper reaction with standard CVD. In PECVD, RF electrical energy is delivered to the process gas or gases to form and sustain the plasma, and therefore, less thermal energy is needed for the reaction.
The dimensions of the IC devices formed by such film deposition techniques have continued to decrease, while the density of such devices on the substrate wafers being processed are increasing. Particularly, IC devices having physical features that are sub-micron in dimension are becoming more common. Furthermore, the semiconductor industry has increasingly desired that such small IC devices have interconnects which are highly conductive. Whereas aluminum alloys and tungsten have been traditionally utilized for conductive interconnects within IC devices, copper has become popular for such interconnects within sub-micron devices. It has been found that IC devices utilizing copper interconnects rather than aluminum or tungsten interconnects, exhibit greater reliability and speed.
For chemical vapor deposition of copper, it has become common to utilize a liquid copper-containing precursor designated in the art as an (hfac) Cu (TMVS) precursor. As is well known in the art, such a precursor, in liquid form, includes a hexa-fluoracetylacetonate (HFAC) organic chemical ligand combined with trimethylvinylsilane (TMVS). The liquid copper precursor must then be vaporized prior to introduction into a CVD processing chamber as a process gas. The use of such metal precursors with organic molecular ligands is broadly referred to as metal-organic chemical vapor deposition or MOCVD.
Processing systems presently available for MOCVD of copper have several particular drawbacks. First, while some systems rely upon bubbling or evaporating the precursor to the gaseous state, other systems rely upon the use of a commercially- available direct liquid injection (DLI) system for delivery of the MOCVD copper precursor to the process chamber. One such DLI system is the DLI-25B available from MKS Instruments of Andover, Mass. DLI systems use liquid from a reservoir or ampule and then heat the liquid in the delivery line as it passes to a process chamber. Pumps and flow controllers are used to manage liquid flow. Such DLI systems are generally not specifically developed for MOCVD copper precursor introduction. In fact, most such DLI systems were developed for delivering water vapor within a process chamber. As a result, processing systems utilizing commercially available DLI systems often result in copper condensation or even deposition within the actual lines and flow control components of the DLI system which hinders introduction of the gaseous precursor to a process chamber. For example, condensation in the line may occur past the point at which the precursor vaporizes but before the process chamber. In addition to the inefficient delivery of the gaseous precursor, particle generation may result within the DLI system which may contaminate a substrate being processed. Deposition within the DLI system accompanied by particle generation will ultimately clog the DLI system and render it ineffective until it may be disassembled and cleaned. As will be appreciated, such factors are undesirable within a processing system as they decrease the efficiency and throughput of the processing system and require additional maintenance.
Another drawback to copper MOCVD systems, as with other CVD systems incorporated within a larger, multi-chamber processing tool, is the inability to control the transmission of CVD reaction by-products from the CVD processing chamber to a substrate handler which interfaces with the numerous processing chambers of the processing tool. The inability to control the by-product flow into the handler often precludes the use of a copper MOCVD chamber in combination in the same processing tool with a physical vapor deposition (PVD) chamber, because such PVD processes are very sensitive to background contamination which is generated by the CVD reaction by-products. With respect to copper deposition, such cross contamination is a significant drawback, because one of the most effective diffusion barriers for copper is tantalum nitride (TaN) which is deposited by a PVD method. Presently, TaN cannot be effectively deposited by CVD techniques. Accordingly, a PVDxe2x80x94TaN processing chamber and methodology cannot be effectively integrated with a MOCVDxe2x80x94Cu processing chamber in a single processing tool unless the contaminating reaction byproducts from the MOCVD chamber can be prevented from entering the PVD chamber.
Still another drawback with current copper MOCVD processing systems results from the fact that such systems allow deposition of copper up to the outer edge of the substrate. Generally, the barrier layer (e.g. TaN) deposited beneath the copper layer on the substrate, which is deposited by a PVD method as discussed above, will not extend to the edge of the wafer. Therefore, a portion of the copper layer which extends around the outer substrate edge, will not be deposited entirely upon a barrier layer. As a result, at the edges of the substrate, the copper will be free to diffuse into the silicon wafer, which may affect the operation of the IC devices formed on the substrate.
Accordingly, it is an objective of the invention to improve MOCVD deposition techniques in general and Cu MOCVD deposition techniques in particular, and thus to present a processing system which addresses the above-discussed drawbacks of current systems.
Specifically, it is an objective of the invention to uniformly introduce a gaseous copper precursor into a process chamber while reducing particle generation from such precursor introduction and reducing clogging associated with prior art precursor introduction systems.
It is another objective of the present invention to reduce cross contamination between adjacent processing systems which are necessary for the various steps associated with IC fabrication from a substrate wafer.
It is still another objective of the present invention to prevent the deposition of copper on portions of the substrate which are not sufficiently covered with a diffusion barrier layer to thus prevent diffusion of the copper into a silicon substrate.
These objectives and other objectives are addressed by the present invention discussed in greater detail hereinbelow.
The system of the present invention addresses the above objectives and provides an improved system for depositing a layer of metal onto a substrate through a chemical vapor deposition process utilizing a liquid, metal-containing precursor. Preferably, the precursor contains copper, and the inventive system may be utilized to deposit a layer of copper onto a substrate.
In accordance with one embodiment of the present invention, the system comprises a process chamber for receiving a substrate in a process space. A vaporizer element is positioned in a vaporization space in the chamber, adjacent to the process space, and is heated to a temperature sufficient to vaporize the liquid, metal-containing precursor into a process gas. A supply of a liquid, metal-containing precursor, such as a copper-containing precursor, is coupled to a nozzle, and the nozzle atomizes the liquid and directs the atomized liquid precursor against the vaporizer element. Temperature control of the vaporizer element maintains the element at a temperature sufficient to vaporize the liquid precursor into a process gas. The supply of precursor, lines delivering the liquid to the process chamber, and the vaporizer element are maintained at room temperature to prevent vaporization, condensation, and possibly deposition in the delivery system.
The process gas is dispersed into the process space proximate the substrate. A gas-dispersing element is positioned between the vaporization space and the process space to disperse the gas. In one embodiment of the invention, a vapor distribution ring having a series of radial holes is utilized. In another embodiment of the invention, a gas-dispersing showerhead may be utilized. Alternatively, both the vapor distribution ring and showerhead may be utilized in conjunction to provide uniform distribution of vaporized process gas into the process space.
The nozzle is coupled to the supply of liquid precursor through a valve which may be controlled by a liquid mass flow meter which controls the valve to deliver the desired liquid precursor flow to the vaporizer element for achieving a desired process gas pressure within the process chamber. Alternatively, a controllable pump might be utilized between the precursor supply and valve for delivering the controlled precursor flow to the nozzle and vaporizer element. With the present invention, all of the components within the precursor delivery system, including the supply, valve, nozzle, and flow control components, such as the flow meter or pump, are maintained at room temperature. In that way, the liquid precursor is only vaporized within the vaporization space of the process chamber proximate the vaporizer element and proximate the process space. As such, deposition within the liquid precursor delivery system is avoided prior to vaporization of the liquid within the vaporization space and subsequent clogging of the delivery system is reduced. Furthermore, since the precursor is not vaporized until the vaporization space inside of the process chamber, the precursor does not have the chance to vaporize and subsequently condense, further interrupting the uniform flow of precursor to the process chamber.
In accordance with another aspect of the present invention, the system includes a temperature control system which is operably coupled to heating elements within the process chamber, and is also operably coupled to the vaporizer element. The temperature control system differentially heats the vaporizer element and the process chamber heating element, such that the vaporizer element is maintained at a different temperature than the process chamber heating element and the chamber walls. More specifically, the temperature control system maintains the vaporizer element at a desired vaporization temperature, such as 60xc2x0 C. for a copper precursor, to ensure proper vaporization of the precursor and to reduce condensation within the vaporization space. The chamber heating element is maintained at a temperature sufficient to heat the internal walls of the chamber above the vaporization temperature of the vaporizer element in order to prevent condensation of the liquid precursor within the process chamber, yet below an upper temperature range to prevent deposition on the chamber walls. Utilizing a copper precursor, the temperature control system is operable to maintain the temperature of the chamber walls approximately in the range of 60-90xc2x0 C., which simultaneously reduces both condensation of the vaporized precursor in the process space, and also reduces deposition on the chamber walls within the process space.
In accordance with another aspect of the present invention, the system comprises an edge exclusion ring positioned within the process space and configured for surrounding the peripheral edge of a substrate placed within a process space. The edge exclusion ring is preferably formed of an electrically insulating material and prevents deposition at the substrate peripheral edge. The ring might also be metal or an insulator-coated metal. The edge exclusion ring overlaps the peripheral edge of the substrate and creates a small gap between the ring and the substrate edge. In one embodiment of the invention, the ring includes a gas passage which is coupled to a supply of an inert gas, such as argon. The passage is configured for directing gas inwardly of the ring and against the peripheral edge of the substrate within the small gap between the ring and substrate edge. In that way, the inert gas keeps the gap between the ring and substrate edge free of the process gas and thus prevents deposition at the substrate peripheral edge.
In an alternative embodiment of the invention, the gas passage may be formed within a substrate stage on which the substrate rests and proximate the outer peripheral edge of the stage. The inert gas stream would then blow upwardly and around the edge of the substrate, and through the gap between the substrate edge and the edge exclusion ring to reduce process gas in that space and thereby prevent deposition at the substrate peripheral edge.
For preventing cross contamination between multiple process chambers within a multi-chamber processing tool, the inventive system incorporates a buffer chamber defining a buffer space therein and positioned beneath the process chamber. A passage is formed between the process and buffer chamber for moving a substrate on the substrate stage between a process position in the process chamber and a buffer position in the buffer chamber. A sealing mechanism engages the passage and is operable to seal the passage and isolate the process space from the buffer space when the substrate stage is in the buffer position. A pumping system is coupled to the buffer chamber for purging the buffer space of contaminants which may leak therefrom and into another process chamber through a common transfer chamber. The buffer chamber incorporates cryogenic panels positioned on adjacent walls of the buffer chamber which are operable for capturing and thereby pumping gas from the buffer chamber to reduce contaminants therein. The cryogenic panels are coupled alternatively to a source of refrigerant or an expander head for rapidly cooling the panels to affect the gas pumping. Preferably, a sensing system is included within the buffer chamber to detect undesired gases to be removed in order to prevent access to the buffer chamber through a transfer chamber until the buffer chamber has been sufficiently evacuated of gas contaminants. In that way, the inventive system may be incorporated within a multi-chamber processing tool with other contaminant-sensitive processing chambers, such as a PVD chamber.
Other features and advantages of the present invention will become more readily apparent from the Detailed Description below.